Comparison of progenitor mass estimates for the Type IIP SN 2012A

We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8 Mpc) irregular galaxy NGC 3239. The photometric evolution is that of a normal Type IIP supernova, but the plateau is shorter and the luminosity not as constant as in other supernovae of this type. The absolute maximum magnitude, with M_B = -16.23 ± 0.16 mag, is close to the average for SN IIP. Thanks also to the strong UV flux in the early phase, SN 2012A reached a peak luminosity of about 2 × 10⁴² erg s^-1, which is brighter than those of other SNe with a similar ⁵⁶Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M(⁵⁶Ni) = 0.011 ± 0.004 M_⊙, which is intermediate between standard and faint SN IIP. The spectral evolution of SN 2012A is also typical of SN IIP, from the early spectra dominated by a blue continuum and very broad (∼10⁴ km s^-1) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Fe II, Sc II, Ba II, Ti II, Ca II, Na I D). The photospheric velocity is moderately low, ∼3 × 10³ km s^-1 at 50 d, for the low optical depth metal lines. The nebular spectrum obtained 394 d after the shock breakout shows the typical features of SNe IIP and the strength of the [O I] doublet suggests a progenitor of intermediate mass, similar to SN 2004et (∼15 M_⊙). A candidate progenitor for SN 2012A has been identified in deep, pre-explosion K^'-band Gemini North Near-InfraRed Imager and Spectrometer images, and found to be consistent with a star with a bolometric magnitude -7.08 ± 0.36 (log L/L_⊙ = 4.73 ± 0.14 dex). The magnitude of the recovered progenitor in archival images points towards a moderate-mass 10.5_{-2}^{+4.5} M_{odot } star as the precursor of SN 2012A. The explosion parameters and progenitor mass were also estimated by means of a hydrodynamical model, fitting the bolometric light curve, the velocity and the temperature evolution. We found a best fit for a kinetic energy of 0.48 foe, an initial radius of 1.8 × 10¹³ cm and ejecta mass of 12.5 M_⊙. Even including the mass for the compact remnant, this appears fully consistent with the direct measurements given above.